This invention relates, as indicated, to torque transmitting fluid couplings, but has reference more particularly to the type of fluid coupling disclosed in Weir U.S. Pat. No. 3,191,733.
In the aforesaid patent, a fluid coupling assembly is disclosed comprising a housing or casing having a hub for rotatably mounting the casing on a drive shaft, a bearing for supporting the casing on the drive shaft, a cover member, a divider plate and a drive disc.
The drive shaft is integrally connected with a coupling flange for coupling the drive shaft to any conventional part of an internal combustion engine, so that if the coupling unit is used for driving a cooling fan, the fan may be bolted to the housing or casing member and the coupling flange may be connected to the pulley which conventionally drives the engine water pump.
The peripheral edges of the cover member engage the peripheral edges of the divider plate, which, in turn, is seated on an annular surface adjacent the periphery of the casing, the cover member and divider plate being clamped to the casing by means of an annular flange of the casing which is swaged or otherwise formed into pressure engagement with the outer peripheral surface of the cover member.
The cover member and divider plate define a fluid reservoir, which is filled with a viscous fluid for driving the housing or casing. The housing or casing and divider plate define a drive chamber within which the drive disc is disposed, the drive disc being press-fitted or otherwise attached to the drive shaft.
The peripheral portions of the drive disc are covered with arcuate facing members, spaced from one another to provide grooves or channels extending between the outer portion of the facing members inwardly across the entire width of the facing members.
The drive disc is provided with a series of circumferentially-spaced ports which extend completely through the disc and are located adjacent the inner margins of the facing members, these grooves and ports providing toroidal circulation of fluid about the peripheral portion of the drive disc, as described in U.S. Pat. No. 2,879,755.
The assembly further includes a resilient blade or spring which is riveted to the inner face of the cover member, a bracket mounted on the exterior face of the cover member, a thermally responsive element in the form of a bimetal strip mounted on the bracket and a thrust member or pin interposed between the bimetal strip and the blade.
Pump means are provided for transferring fluid between the reservoir and the drive chamber, said means comprising an abutment member or weir of cylindrical configuration which extends into but is movable within an aperture in the divider plate. This aperture is extended to form a port which provides fluid communication between the reservoir and the drive chamber, the abutment member trailing the port in the direction of rotation of the divider plate with relation to the drive disc.
The position of the abutment member is controlled by the aforesaid resilient blade, to which the abutment member is secured. The position of the blade is controlled by the bimetal strip, which is so arranged that upon an increase in temperature ambient to the bimetal strip, the central portion of the strip bows outwardly and bears against one end of the thrust member, the other end of which bears against the blade. The mounting of the blade is such that its inherent resiliency urges it against the inner end of the thrust member.
In operation, the reservoir is filled with a fluid, such for example, as an oil, to a degree sufficient to fill the spaces in the drive chamber between the opposing surfaces of the facings and the adjacent walls of the divider plate and the casing or housing. Preferably, the minimum quantity of fluid is such that fluid may flow through the apertures in the drive disc providing the toroidal heat dissipating circulation of fluid, which has been mentioned. With the cover or housing rotating, centrifugal force distributes the fluid to a uniform level within the reservoir and the drive chamber, the fluid passing freely through the port. The rotational speed of the casing or housing, as compared to the rotational speed of the drive shaft, that is, the degree of coupling between the two, is dependent upon the amount of fluid in the drive chamber.
When the temperature ambient to the bimetal strip is relatively high, indicating that a maximum degree of coupling between the casing or housing and the drive shaft is desirable, the inner face of the abutment member does not extend into the path of fluid in the drive chamber, and therefore the pumping means formed by the abutment is inactive and centrifugal force maintains the fluid level uniform within the drive chamber and reservoir, the drive chamber, under these conditions, having a maximum amount of fluid therein and therefore a relatively high degree of coupling between the drive shaft and the casing or housing.
When the temperature, ambient to the bimetal strip decreases, indicating that a decreased degree of coupling between the drive shaft and the casing or housing is desirable, the central portion of the bimetal strip moves the thrust member inwardly and consequently the abutment member inwardly to position it so that it extends from the inner surface of the divider plate into the drive chamber and into the path of fluid in the drive chamber. With the abutment member thus positioned, it acts as an impact type pump, raising the fluid pressure in an area just ahead of, or leading, the abutment. The consequent increase in pressure in this area drives or pumps fluid from the drive chamber through the port and into the reservoir thereby reducing the volume of fluid in the drive chamber and, as a result, the degree of coupling between the drive shaft and the casing or housing. This movement of the abutment member places the pumping means in an active position in which it is capable of removing fluid from the drive chamber and transferring it through the port and into the reservoir.